The major objective of this research program is to delineate the effects of 3 temporal parameters of response-produced drug: delay between response and drug, frequency of opportunity for drug production, and rate of drug infusion. Squirrel monkeys will be trained to make a key-press response that will produce, according to a schedule of reinforcement, and infusion of drug solution through a permanent intravenous catheter. Several different CNS stimulant drugs, including cocaine, d-amphetamine, phenmetrazine, and methylphenidate, will be studied at a variety of doses. Both overall rate and temporal pattern of responding will be studied, and changes within as well as across experimental sessions will be computer analyzed. Changes in behavior maintained by infusion of each of the drugs will be examined as a function of (1) delay between the required key-press and drug infusion; (2) the spacing out of opportunities for drug infusion; and, (3) the rate of infusion of each drug (mg/sec). The study of these temporal parameters will elucidate the interaction of drugs as consequences of behavior with the direct effect of a drug on subsequent behavior.